The present invention is directed to an optical cable which includes at least one optical light waveguide arranged loosely or fixedly in a protective covering or sheath and at least one support element.
Cable constructions with light waveguides have a general difficulty which consists in longitudinal changes, which are often due to shrinkage, very readily occurring either during or following thermal stresses, and these changes raise the attenuation in the waveguide as a consequence of impermissible bending of the waveguide. It is known to surround a light waveguide such as optical fibers themselves with longitudinally stabilizing securely positioned coverings or sheaths. In addition, an optical fiber is known from German O.S. No. 27 28 658 in which the optical cable has at least one optical fiber or light conducting waveguide which is stranded with support elements with at least one support element being disposed in the center of the cable. The core of the cable, which consists of the support elements and the light waveguides which are preferably arranged in hollow sheaths, is externally covered with a plastic band or jacket and is surrounded by a cladding or sheath consisting of a particularly resistive plastic.
The support elements, which are intended to primarily prevent a short radius bending of the light waveguides as a consequence of a longitudinal shortening of the covering sheaths or shells, thus satisfy other tasks than the conventional support elements. For example, instead of just protecting the light waveguide against tensile stresses, the support elements must be decentrally stranded or cabled in a specific cable construction so that in addition to the support effect, they may also provide a satisfactory flexibility. Insofar as they must be fully insulating, only stranded or twined threads or yarns can be considered for this purpose.
However, the difficulty which arises here is that such threads, which are stranded together without a corresponding hardening or bonding agent to securely seal or cement the individual threads or yarns together exhibits no supportive effect whatsoever in the case of a longitudinally directed compressive forces. To retain the flexibility of the cable, the individual support elements cannot be permitted to become cemented to each other. Also no mechanical connection is permitted to arise between the light waveguides or their covering such as the sheath or envelope and the support elements, which connection would influence the flexibility of the cable in an unfavorable manner.